Loop Heat Pipe Wick Fabrication via Additive Manufacturing

As the capabilities of CubeSats and SmallSats increase so do the heat rejection requirements. While loop heat pipes (LHPs) are capable of transporting heat across deployable radiators they are currently too expensive for most applications. The largest cost comes from the fabrication of the primary wick which requires multiple machining steps as well as a knife-edge seal. The focus of this work is the development of a 3D printed LHP evaporator using a direct metal laser sintering (DMLS) process to fabricate the primary wick. 3D printing LHP wicks offers several advantages. The overall cost can be significantly reduced by eliminating multiple machining steps, and the risk of failure can be reduced by eliminating the knife-edge seal. The challenge with 3D printing of LHP primary wicks is that a very small pore radius is required to supply sufficient capillary pumping power. A pore radius and permeability study was conducted for optimization of DMLS methods and parameters for fabricating primary wicks. The result of this study is DMLS parameters for wicks with pore radii less than 10 µm. In addition, a DMLS parameter optimization study was performed for fabrication of the coarser secondary wick. Experimental testing is being completed on a complete LHP prototype with 3D printed primary wick fabricated using the optimized DMLS parameters. Modeling is being completed to optimize the design of the primary wick using geometries that are compatible with DMLS. Life testing has begun to demonstrate compatibility of the 3D printed stainless steel wick with ammonia.